The purpose of this study was to examine our hypothesis that gamma-aminobutyric acid (GABA) in the nucleus tractus solitarii (NTS) may be related to the hypoxic ventilatory decline (HVD) and that chemoreceptor stimulation was essential to activate this mechanism. We used unanesthetized, freely moving rats in this study. An in vivo microdialysis technique was used to measure the extracellular GABA concentration ([GABA]o), and an in vivo microinjection technique was used to examine the effects of the GABA agonists and antagonists on the ventilation during hypoxia. The GABA agonists injected into the NTS attenuated the ventilation during hypoxia. By hypoxic exposure, [GABA]o was increased during the HVD. However, by carotid body denervation (CBD), this GABA increase was abolished. Although GABA antagonists microinjected into the NTS during the HVD phase significantly increased the depressed ventilation, this effect on the ventilation was abolished by CBD. These results suggest that the GABA in the NTS has a pivotal role in the HVD and that this mechanism is not activated without chemoreceptor stimulation.
Medical students may be less likely to correctly identify S2/S3/S4 as compared with heart murmurs in a situation close to clinical setting even immediately after training. We may have to consider such a characteristic of students when we provide them with cardiac auscultation training.
The exact nature of asleep blood pressure in relation to awake blood pressure is still unclear in patients with obstructive sleep apnoea. This study aimed: 1) to investigate the asleep blood pressure in both apnoeic and ventilatory periods; 2) to determine the diurnal and nocturnal factors correlated with the changes in blood pressure from apnoea to ventilatory periods during sleep.Thirty-two patients, newly diagnosed as moderate to severe obstructive sleep apnoea with a standard nocturnal polysomnography, were enrolled. The blood pressure was monitored by using the noninvasive continuous monitoring method during polysomnographic study.The mean blood pressures in ventilatory periods during nonrapid eye movement (NREM) and rapid eye movement (REM) sleep were 117.517.9 mmHg and 128.8 21.9 mmHg, and those in apnoea periods were 94.515.4 mmHg and 102.719.0 mmHg. The average blood pressure during NREM sleep (103.016.1 mmHg) was higher than the awake blood pressure (97.015.7 mmHg). The blood pressure during REM sleep was greater than that during NREM sleep. The changes in the nocturnal blood pressure from apnoea to ventilatory periods were inversely correlated with the age and nocturnal mean nadir saturation.In conclusion, patients with obstructive sleep apnoea have higher asleep blood pressure than awake blood pressure.
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